The touch screen technology has been widely used recent years in computing devices, such as mobile phones, notebook computers, and variety of portable electronic devices (such as game console, multimedia players, and the like). With this technology used in the user-interface, interaction between user and the computing device become more convenient and efficiency. Instead of using a mouse, keyboard, or any other intermediate devices, users can interact with what is displayed directly. Some touch screen can not only controlled through single or multi-touch gestures but also detect specially coated gloves and stylus.
Among a variety of different touch screen technologies, capacitive touch panels became more popular after the releases of new portable electronic devices. Unlike the surface capacitive touch panels can only detect single touch, the projected capacitive touch (PCT) panels are capable of implementing multi-finger touch detection. The PCT technology makes multi-gesture control possible like enlarge, narrow, rotate, or drag a pattern on a projected capacitive touch panel simultaneously.
Projected capacitive touch screens are made up with a matrix of rows and columns of resistive transparent conductive material such as indium tin oxide (ITO) layered on sheet of glass. The two axes of conductive material are driving electrodes and sensing electrodes. Capacitance exists among them.
As the human body is also an electrical conductor, touching the surface of the display results in a distortion of the screen's electrostatic field. There is a change in the level of capacitance. The chips measures cross-capacitive in the X-axis and Y-axis of a projected capacitive touch screen structure and for every intersection of the drive/sense lines the capacity change is interpreted and converted to XY coordinates that correspond to the actual touch position.
One of the most important cost drivers in touch screen design is the border area. Unlike traditional analog touch screens that have four or five signals lines, projected capacitive touch screens often have forty or more connections; this is due to each row and column needing at least one connection requiring the border to extend past the active area of the touch screen.
The driving IC of projected capacitive touch screen contains three sections that are driving, sensing, and micro-programmed control unit (MCU). There are two main driving modes in the driving section. One is only the selected driving electrode will be forced a high voltage AC signals and other driving electrodes are connected to a fixed DC level (ground, VDD, or other DC level). The IC process is complex and power consumption is high of this mode. The other mode is to provide a 5V AC signals to the selected driving electrode and other driving electrodes are connected to floating signals. Although the IC process is simpler, it will become a big problem for the determination that whether the sensing node on that sensing electrode has been touched and additional calculation need processed by micro-programmed control unit (MCU). The two driving modes mentioned above could not use if driving electrodes have high resistance because of the attenuation of signals caused by parasitic capacitance.
In this technology, normally the two driving electrodes adjacent to the selected electrode are provided the same AC signals as that to the selected one. While in prior design, only selected driving electrodes (N) will force AC signals, others driving electrodes are connected to a fixed DC level (ground, VDD, or other DC level). In this technology, the selected electrode (N) and its adjacent driving electrodes (N−1, and N+1) have the same AC signals, other driving electrodes are connected to a fixed DC level. This novel driving algorithm can significantly minimize the parasitic capacitance so a lower AC voltage can be used as driving signals at driving electrodes have high resistance. In this case, the present invention is able to apply to a large-scale touch panel, reduce the material cost, complexity of IC process, and power consumption.